Flow control is an integral part of robotic sealant applications. For a typical robotic sealant application, the robot velocity signal is used to control the flow rate of a sealant dispensing pump which is driven by a DC servo motor. Heretofore, a positive displacement pump has been used to control sealant flow since average sealant flow is then governed essentially by the piston area and the linear velocity of the piston. Because of the compressibility of most sealant materials and elasticity of sealant hoses, the flow rate always lags behind the velocity command of the piston. Also, factors such as temperature and nozzle wear affect the lag. Therefore, an inconsistent sealant bead occurs. An alternative control, such as exclusively using pressure control of sealant flow, is unreliable because of the many uncontrolled variables as, for example, temperature change, nozzle wear, viscosity changes, etc.
Even placing a flowmeter very near the output nozzle and forming a closed loop flow control does not provide a satisfactory solution since the variability of the parameters within the loop affects the loop stability.